Joint replacement, or arthroplasty, is a surgical procedure in which the diseased parts of a joint are removed and replaced with new, artificial parts. Presently, these artificial joint components are being produced from improved materials such as highly cross-linked polyethylene, metal-on-metal, and ceramic-on-ceramic. After the joint replacement, osteolysis is a major problem and is believed to be due to an inflammatory process brought on by particulate matter or debris dislodged from the implants themselves. In total hip replacements for example, some degree of osteolysis is present in up to 40% of all cases within 10 years of surgery.
Healthy animal joints have an extremely low coefficient of friction and little wear due to cartilage and natural lubricants (e.g. body fluids) formed between joint components. Such minimal friction is difficult to achieve with engineered artificial joints. One problem that contributes to increased wear in artificial joints is a lack of sufficient lubrication between contact surfaces of the implant. The resulting friction produces wear debris that is an important contributor to pathologic tissue response. Therefore, the long-term threat to component failure from a biologic standpoint is this increase in wearing debris associated with osteolysis from a lack of sufficient lubricating matter between surfaces of the implant. The critical initiating sequence involves the interaction between small particulate materials and responding specialized cells that causes destruction of the bone surrounding the implant and loosening of the implant. The number, size, distribution, and type of particulate material are also believed to have an effect on the process.
Designing patterns of channels, cavities or a combination thereof at the contact surface of an implant provides a mechanism to contain an increased volume of lubricating material at the point of contact between implant components. Previous attempts to produce such patterns have used monomer ion beam methods. These monomer ion beams produced deep trenches with rough edges that resulted in increased wear debris as particulate matter from the rough edges flaked off.
In general, surface roughness of artificial joint components can also increase friction between the contact surfaces of the implant and can attribute to wear debris. However, surfaces of artificial joint components having patterns for lubrication purposes are inherently irregular and non-planar and can be difficult to smooth using conventional processing techniques.
Any particulate debris from implanted joints can cause undesirable tissue reaction as well as promote accelerated wearing out and failure of the implants themselves.
It is therefore an object of this invention to provide surface patterning on artificial joint components to provide a more consistent level of lubricating matter between the wearing surfaces.
It is another object of this invention to provide smoothing of a patterned artificial joint component surface.
It is a further object of this invention to provide surface modification of artificial joints by gas cluster ion beams to alleviate the problems associated with component wear and osteolysis.